Bone anchors can be used in orthopedic surgery to fix bone during healing, fusion, or other processes. In spinal surgery, for example, bone anchors can be used to secure a rod or other spinal fixation element to one or more vertebrae to rigidly or dynamically stabilize the spine.
A fastener is typically applied to the bone anchor to reduce the rod into a rod seat of the bone anchor, to secure the rod to the bone anchor, or to lock one or more degrees of freedom of the bone anchor. Exemplary fasteners include set screws that are threaded into a proximal end of the bone anchor and closure caps that are secured to the bone anchor by quarter-turn rotation. A driver instrument is generally used to apply the fastener by applying a rotation force to the fastener.
When installing the fastener, the surgeon must be careful not to drop the fastener into the surgical site, particularly in the case of minimally-invasive procedures where it can be difficult to retrieve a dropped fastener. Driver instruments with a split tip or a retention spring have been developed to prevent the fastener from separating from the driver instrument, however such instruments may not be conducive to applying the high levels of torque needed to achieve final tightening of the fastener. Instead, the surgeon must typically switch to a solid-tipped driver instrument before final tightening. Also, in the case of threaded fasteners, handle designs that facilitate application of high levels of torque for final tightening may not be the most ergonomic design for quickly advancing the fastener along the threads during intermediate tightening. Accordingly, surgeons often use three or more different drivers for applying the fastener: a first driver for initial placement of the fastener, a second driver for intermediate tightening of the fastener, and a third driver for final tightening. This can make installing the fastener cumbersome and time-consuming, potentially leading to surgeon fatigue, poor ergonomics, and lengthened surgical times.